Dresden 2017 – wissenschaftliches Programm
HL 25.20: Poster
Montag, 20. März 2017, 15:00–19:00, P2-OG2
The effective potential energy drop as a control parameter for the sheet carrier density of two-dimensional electron gases in AlGaN/GaN heterostructures — •Dennis Mauch, Heiko Bremers, Uwe Rossow, and Andreas Hangleiter — Institut für Angewandte Physik, TU Braunschweig, Germany
We introduce the effective potential energy drop in AlGaN/GaN heterostructures as a control parameter for the sheet carrier density of two-dimensional electron gases (2DEG). As a consequence of the noncentrosymmetry of the wurtzite structure in group-III nitrides and the large ionicity factor of the covalent metal-nitrogen bond, a large spontaneous polarization is oriented along the hexagonal c-axis. In addition, group-III nitrides are highly piezoelectric. Hence, in AlGaN/GaN heterostructures, where the AlGaN layer is grown pseudomorphically on top of GaN, strain leads to piezoelectric polarization in the AlGaN epitaxial layer. Under certain conditions, the induced electric fields, due to polarization discontinuity at the heterointerface, give rise to the formation of a 2DEG. We also investigated the influence of an additional AlN-interlayer at the AlGaN/GaN interface in order to reduce alloy disorder scattering and thus to reach higher 2DEG mobilities. The samples were grown in our commercial MOVPE system/reactor on c-oriented sapphire substrates. The electrical properties were obtained via Hall effect measurements at room temperature using the van der Pauw configuration, and the structural details via HR-XRD. Our aim is to optimize these structures to highest mobilities and small sheet carrier densities down to the quantum Hall regime.